Process of blasting



p 1952 D. M. M FARLAND PROCESS OF BLASTING Filed May 16, 1946 Fig. 5-

David M. McFarland,

IN VEN TOR. fizz 57% Fig.2

reduced vibration conditions.

Patented Sept. 9, 1952 PROCESS OF BLASTING David M. McFarland. WestGhester, Pa., assignor to Atlas Powder Company, Wilmington, Del., a

corporation of Delaware Application May 16, 194 Serial No. 670,193

' "'14 iGlaims.

' *frhe present invention relates to blasting conditions of backbreak,

- A-iurth'er object of the invention is the provision of a method ofblastingproducti-ve of "Still another object of the present invention"is--the provision of a -method of blasting pro- "ductive of lessenedthrow of 'brokenmaterial.

'Qther'objec'ts oiithe invention will be apparent fromthefollowi ngdescription. 7 4 v I *Blasti-ng operations of any considerable size,-*snchas,"for example, quarrying-{or the fproductioniof stone suitablefor crushing,- are usually cohductedby detonating explosive charges in aenmity-peter; holes drilled in -a row behind and generallyparallelto aiace. The explosive charges in the individual bore holes areconventionally piactically simultaneously-initiated by such means-aselectric blasting caps-or detonati-ng fuses. The-blast pushes out theburden in front "oi-the holes" creating a i new race along the l-ineo'fbore holes.

It is desirable that the blast break the blasted material into sizeswhiehperm'it ready removal "by power shovels, drag-lines, or-otherloading 'equipmen-t. Usually,'howeven-customary blasting operations,such as have been just described, res'ulti'na throwing out of much ofthe burden "in large"solid blockswhich cannot beadequa'tely handled butwhich :must be individually further drilled, charged "with explosives,and blasted to break them up into manageable sizes (secondary blasting).i

dinotherdisadvantage which commonly results from-the customary methodofblasting described above istheioccurrence of a large amount ofbackbreak. Backbreak is the formation of an uneven -face and of largecrevices which extend into the newly created face. "Backbreak is antioning, drilling, and loading of a new line of bore holes. Third,crevices permit wastage of explosives in subsequent blasts due topremature escape of gases through the crevices without effective actionon the burden;

Customaryblasting technique is productive of another serious ,difiicultyin the'vi-brations produced. Many quarries and other blasting sites arelocated near inhabited or manufacturing areas, and the vibration wavesset up by blasting are blamed for much damage to structures andequipment. To prevent complaints, many quarries must seriously limit thesize and number of bore holes in each blast despite the fact that forbest blasting efficiency a large number of bore holes in a blast isdesirable.

A further dilhculty often encountered in blasting operations isexcessive throwing of the blasted material. Undue throw often coverstracks used for haulage or damages equipment, and in spreading theblasted material over too large an area, makes its subsequent handlingslow and expensive.

According to the present invention, a method is provided by which theabove-mentioned disadvantages are ;-in a large measure avoided.

It has been found that if, in ablastof a row of at least threebore holesaligned'to break through a face and -f orm a new face therebehind, theexplosive charges in adjacent bore holes are detonated at slightlydifiering times the action of the blast is usually radically alteredwith the production of much improved breakage, greatly reducedbackbreak, a most considerable diminution of "vibrational efiects,-andmuch reduced throw. v

Firing time separations should not be sumcientlygreattha-t the unity ofthe blast and the well known; desirable actionof multiple hole blasts onthe burden are destroyed, and separations which are productive ofoptimum results vary somewhat with the nature of the material beingblasted. In general, separations as high as about 150 milliseconds andas low as about '2 milliseconds produce improved'results, but it isusually preferred that the amount of separation lie'between about204*millisec0nds and about 75' milliseconds.

As will hereinafter be more fully described, the firing'timeseparaticnsemployed in accordance withthe present invention may be obtained by anumber of diiferent means, as for example, by the use of electricblasting caps havingljdifferent firing times, electric blasting capsconnected'to difierent circuits which are energized .the. explosivecharges in adjacent holes. usually-preferred, however, that-all holes ina first firing bore hole.

after the actuation, in each hole of the first group, of the detonationinitiator therein. For example, the bore holes of a first group mayadvantageously be initiated by means ofinstantaneous electric blastingcaps in a single circuit,

while the bore holes of a second group, each of which is in alternatingposition with a bore hole of the first group, are then initiated at atime or times slightly separated from and after the time of initiationof the bore holes of the first group by means of short delay electricblasting caps connected in the same circuit as the instantaneouselectric blasting cap utilized to initiate-the bore holes of thefirstgroup. In this manner all of the explosives in theblast may bedetonated within a very short time period, as from about 2 to about 150milliseconds and preferably from about to about "75 milliseconds,

and firing time separations of the same order between the initiation ofthe explosive charge in each bore hole and the initiation of the chargeor charges in the hole or holes adjacent to'it may be positivelyobtained.

Since it is chiefly important that firing of adjacent holes be separatedby times within the effective range, desirable blasting effects may alsobe obtained without the alternating scheme just describ ed. Thus a blastaccording to the invention is conducted when a second'hole is firedafter a first hole and a third hole is fired after a second hole,provided that the difference in firing-time between adjacent holes iswithin the effective range. The difierence in firing time between thefirst and third holes may be outside the effective range. e

Moreovenas it is the time difierential between adjacent holes thatis'important, it can be seen .that it is not necessary to fire any holeat substantially zero time after the actuation, in each ,hole', of thedetonation initiator therein. Thus, where the bore holes are grouped andinitiated in alternating relation, as described above, there -may be atime interval or delay between'the initiation of the blasting capsrelied upon to initiate the bore holes of the first group and theiractual initiation of the bore holes, provided that the time interval ordelay between the initiation of theblasting caps relied upon to initiatethe bore holes of the second group is longer and provides the properdifferential between the initiation of It is blast which are fired inaccordance with the process of the present invention be fired within asshort a time as is practicably consonant with the obtention of efiectivetime separations between adjacent holes.

ing difiering firing times it is desirable that the ing to the presentinvention may be obtained in any convenient manner, it is usuallypreferred to obtain them by means of delay electric blasting caps havingparticularly short delay periods not greater than a few tenths ofasecond and 4 preferably not greater than about 3001 millisecf onds.

Delay electric blasting caps, as is well known in the art, are blastingcaps which fire a de- 1 layed period after the application of current toI them. Most delay" electric blasting caps obtain their delay period bymeans of a fuse train 10- cated between the ignition material and theprimary detonating composition in the cap, and the delay time isdetermined by the burning time of the fuse train.

While particular short delay electric blasting caps form no part of thepresent inventionit may be explained that a preferred short'delay:electric blasting cap may be provided by interposiiig V a fuse element,or delay train, made up of a metal tube into which is pressed a'chargeof black powder, between an initiating means such as an electric matchand a primary detonating explosive in the cap. When the delay train ismade'of a metal tube 0.140 inch in diameter and T's inch long into which30 to;96 mesh granular black powder is pressed under about ,450 poundsto a height of about 0.068, inch, a delay period averagingabout 40milliseconds with a standard deviation (the square root of the sum ofthe firing time deviations of a number of caps from the average delayperiod of the caps divided by the number of caps i. e. the .rootfmeansquare deviation) therefrom of about 16 milliseconds is obtained. Capsof this type will hereinafter be designated as A type 'short delayelectric blasting caps. When somewhat more black powder is employed sothat the height of; the black .powder charge, is about 0.133 inch andwhen an electric match is spaced about inch above .the metal delay tube,a short delay electric blast- "called B type short delayelectricblasting caps.

The shortdelay electric blastingcaps just described are carefully sealedand are not vented as is customary in conventional delay electricblasting caps of longer delay periods employing, black powder delaytrains, for thebuilding-up of pressure in the caps is generallyimportant towthe development of high burning rates; 7, .1, f v Delayelectric blasting caps'applicableiorzuse in the present invention aremore specifically: described and claimed in co-pending application,Serial No. 682,995, filed July 12, 1946, byJohn E. Jefiery for DelayElectric Blasting Caps;

It is to be particularly noted that shortdelay electric blasting caps asdescribed above normally vary somewhat-in delay period. The variation intiming is in each case: within the effective range of time separationrequired for the present inven,- tion. It can be shownbyconventionalstatistical methods that when'caps having a standard deviation of 16milliseconds, such as the A or B-caps noted ab ove, are distributed at"random among a series of bore holes, %,of the-adjacentholes will beexpected, to fire with time separationswithin the limits of about 31nilliseconds andabput 37 milliseconds ee simpps Engineers Manual ofStatistical Methods, 1941., John Wylie & Sons, Inc., New York,especially chapter XII and appendixC). Hence the invention may bepractice'd by initiating a row of holes by means of a number ofsimilarly prepared shortdelay electric blasting caps when the individualvariations in firing times among the caps are adequate to providethedesirable effects. i I

Another method by which the present invention may be employed makes useof ordinary instantaneous electric blasting caps connected to differentcircuits, the flow of current in which is initiated at spaced times byelectrical or mechanical means which close the different circuits ashort time apart. A multiple switch blasting machine is an example of afiring means which may be used when the invention is performed inthismanner. I

The multiple circuit method of obtaining the delay means, as justdescribed, is not preferred for use in some formations where the firingof the holes in the first circuit may lead to the breaking of the wiresof the second circuit before that circuit is energized, 'for'under suchconditions misfires in the second circuit may wellre sult; Delayelectric blasting capsarenot subject to this disadvantage since they mayall be initiated at the same time when connected in single circuit. l

A further manner in which the present invention maybe practiced is bythe use of detonating fuse. Normally when detonating-fuse is used, atrunk line of detonating fuse is connected to branch lines which run toindividual bore holes. By varying among the different'holes the lengthof fuse extending from a bore hole to a trunk, thertime of initiationvof difierent holes may be easily varied. to provide the desirableeffects of the present invention. However, since detonating fusedetonates at an exceedingly high velocity, the obtention of the desiredvariation in firing times requires the use of very considerable-lengthsof fuse, and the practice of the invention by this last-mentioned meansis not usually preferred. v

Another manner in which detonating fuse may be used to produce theeffects of the present invention in a substantial way is by initiating along row of bore holes by means of two trunk lines of detonating fuse.One trunk line may be connected to branch lines leading to one group ofalternating holes, and the other trunk line may be connected to otherbranch lines leading to the other group of alternating holes. The trunklines may be then initiated from opposite ends of the row. It may beseen that in this way the greater number of the adjacent holes aredetonated at separated times. This same general method may be performedwith a single blasting cap if the trunk line of detonating fusedetonated by it is joined to the other trunk line at the opposite end ofthe row. 7 V

The present invention is not limited in its application to blasting witha single row of bore holes, but may be applied where more than one rowof holes parallel to a face are fired. When multiple rows are employed,it is preferred for the obtention of optimum effects that each row ofholes be shot with a variation in timing amongst the holes as set forthabove in describing single row blasts. Also when multiple row blasts aremade it is usually preferable to time the firing such that holes insuccessive rows fire somewhat behind holes nearer the blasting face. Theinventionfinds application in many different types of blastingoperations. A number 6 of these will be described inconnection with: the

drawings inwhichx l I Figure l is a diagrammatic isometric view of aquarry face withbore holes drilled therein. 7

1 FigureZ is av diagrammatic cross sectional view ofa loaded borehole.

.Fig'ureB is a. diagrammatic isometric view ofa bank. provided withhorizontal bore. holes. Figures is a diagrammatic. elevational view-ofatun'nelfacaandi y 5 I Figure 5 is. a cross sectional View taken on line5-.5 of the face shown in Figure 4 I g For quarry blasting shots it isusuallyfpre ferre-d that a line of holes ll' be drilled generallyparallel to a vertical quarry face l3 as shown in Figure l. .-In apreferreduse of the invention bore holes such as-are shown in Figuralare initiated. by :a series of shortsdelay electric blastingficap's oftwo different periods arranged in alternating relation. Thus onegroup ofalternating bore holes may be initiated by means of A type short delay.electric blasting caps while-the intermediate group may be initiated byB type delay electric blasting caps, or short delay electric blastingcaps maybe alternated with'instantaneous blastingcaps; In an alternatingsystem of blasting it is usually preferred that the timesof initiationbe arranged so that the hole nearest an open end of a row be firedbefore its adjacent holes.

According to another method of operation, each hole can. be fired bymeans of short delay'electric blasting caps which have a normalvariation in firing time amongstthem of an-amountsuf ficient to produceeifective'time separation Often in quarry blasting it is desirablethatmore-than one row of. holes paralleltoaxface be employed. The setup forsuch a blast would look similar to that shown in Figure 1' except thatat least one more row of holes would appear behind those already shown.vMultiple row blasting provides an opportunity for combining blastingoper-. ations accordingto the present method withmore conventionalblasting operations, although it is usually preferred that all holes befired in accordance with the present invention. Thus a front row ofholes might be fired with instantaneous electric blasting caps or withalternating instantaneous electric blasting caps and A type short delayelectric blasting caps, while a back row might be fired with "13 typedelay electric blastmg caps.

In Figure 2 is shown an exemplary loading scheme for bore holes such asmay be employed according to the present invention. In the bore hole,represented generally at 20, is shown a main explosive charge 22, acharge of gravel stemming 24, an explosive deck charge 26, a furthergravel stemming charge 28, a second explosive deck charge 39, and afinal stemming charge 32. The bore hole is initiated in the main chargeby means of two similar electric blasting caps 34 and 36 to whichcurrent is led by wires 38 and Ml, each of which includes two individualleg wires 42 and M, and it and 48. The deck charges are initiated fromthe main charge by means of a line of detonating fuse 50 running fromthe main charge to the top deck charge.

The present invention is not limited to any particular loading'schemes.That just described has been found productive of particularly goodresults but other systems may be employed. For example, the individualholes instead of being directly initiated by electric blasting caps maybe initiated by lines of detonating fuse which are a 7 in-turn initiatedby means of electric blasting caps located either inside or. outside thebore holes.

In Figure 3 is shown .a setup for horizontal blasting such as is used ina stripping. operation where a seam of coal is to be uncovered.Horizontalholes are drilled into a bank I 3 and generally .parallel.tothe. material to be uncovcred.- Usually it is preferred when the bank ishigh also to drill a row of vertical holes ll.

.Thefiring of a .row of horizontal holes in a stripping blast accordingto the invention finds particular advantage because it is oftenproductive of'much less undesirable shattering of the material to beuncovered. The improved breaking and vibration conditions effected-bythe present' invention are, of course, also important in strippingoperations; When vertical holes are employed in addition to horizontalholes they alsomay be fired according to the present invention, or theymay be so fired and thehorizontal holes fired conventionally.

It should be noted that in stripping operations where both horizontaland vertical holes are shot. it is often desirable that one of theseries be fired somewhat ahead 'of the other. .Whether a horizontalseries or a vertical series is fired first usually depends upon thehandling equipment which is available for. removal of the blastedmaterial.

- For example, a horizontal row of holes might be fired with alternatinginstantaneous electric blasting caps and A type short delay electricblasting caps while a vertical row of holes might be fired by means ofB" type short delay blasting caps.

In some stripping blasts,.-it is desirable to provide multiple rows ofeither orboth of vertical and horizontal holes.

Figures 4 and 5 illustrate a setup for use where the process of theinvention is employed in underground work. Figure 4 represents a frontelevation of the face l3 of a tunnel with a row of holes I l drilledacross it. As appears from Figure 5,. therow of holes. is: drilled.downwardly and at an angle. In this way the lower corner of the face isblastedout. 'Ihe'individual holes in the row are discharged at anumberofseparated times within. the effectiverange'. .In angle blasting ofthis'typ'e fit is usually preferred that the angle made by the .holeswiththe face be not less than Subsequent rows; or holes may-be drilledparallel to the, row just described; -.The invention will be further;illustratedby the. following examples which, describe specific blastingoperations: Example!" A, blast was made in a quarry from which amassivehblue dolomitic limestone is mined and crushed for firing. Thestone at thisparticular quarry has long been noted for being especiallyhard to break up into manageable sizes without excessive secondaryjblasting. A line ofseven seveninch diameterholes was drilled accordingto the general scheme shown in Figure '1 of the drawing. Each hole wasloaded principally with low;veloc ity 60% strength dynamite in thegeneral manner shown in Figure 2 of the drawing except that five of the.holes were supplied with a third'deck charge. 1 Theexplosive for all butthe top deck charge was in the form ofsix inch diameter 25 poundcartridges. 1% by-8 inchfcars tridges were used to make up-the top deckcharge. The stemming was finely crushed stone. Each hole was initiatedin thermain charge by two primer cartridges each made up of a shortdelay electric blasting cap embedded in a 1% by 8 inch dynamitecartridge. Oneprimer was inserted just prior to the second cartridgeloaded into the hole, and the other primer wasinserted just prior to thelast cartridge ofv the main charge; Primacord detonating fuse was usedto'carry detonation from the'main charge to r. the deck charges. Morespecific data relative to-the charging of the various holes is'set forthin the table below. The blasting caps were all fired in a single series.V a

7 TABLE Distance Distance Estimated Weight of H01 8 No Hole Height fromfrom weight Dynamite Depth of Face Hole to Preceding of a in Main Face 1Hole Burden Charge ft. ft; ft. tons lbs.

61 56 v 14 1 24 1, 568 325 62 57 13 17 1,049 350 62 57 13 17 l, 049 32562 57 13 18 1,111 325 63 58 13 16 1, 005 3 325 63 I 58 13 17 1,068 35063 '58 12 17 986 350 1 Distance from termination of preceding blast.

Depth of Weight of Depth of Weight of De th of Wei ht of Height ofbottom of crgplosive bottom of explosive botFom of expfiisive Hole No.mam first in first f 'second insecond top. intop' charge deck deck deckdeck deck deck charge charge charge I charge charge charge It. ft. lbs.lbs; t. be. 1 3O 12% 12% f G l 5 f. 33 r 37% 6. 6 3 32 50 none '6 5 4 3350 37361 6 5 5 i 26., 50 none 1 6 5 6 33 50 37% 6 5 7 as a 7% 6 Theshort delay electric blasting caps used were of the A- type. his to benoted that the time separation between adjacent holes is lessened whentwo short delay electric blast- ;ingcaps are employed in each hole, asinthis example. The expected separation under these conditions is thevalue obtained for the use of zone cap in a hole, as noted above,divided by the square root of two; Thus, when two caps are 'usedin eachhole if the caps are from a group having a standard deviation of 1-6 itwill beer;- pected that in at least 90% of the cases the sep- :arationin firing time between adjacent holes will be at least about 2milliseconds.

When the blast was set off very little vibration was'noticeable and thenoise was greatly mufiied as'compared with instantaneously fired blasts.The breakage obtained was excellent as evidenced bycomparison'with agenerally similar blast made immediatelyprior and adjacent to it andinitiated entirely with the use of instantaneous electric blasting caps;After the prior blast it was necessary that 198 holes be drilled in theblasted rock for secondaryblasting operations. After the blast of thisexample only 19 holes were drilled for secondary blasting.

Example Ii Another blast was made in the same quarry as that in whichthe blast described in Example I was made. The manner or loading thisblast was generally similar to the blast of Example I However, in thisblast each of the 1st, 3rd, 5th, and 7th holes was initiated by meansofinstan= taneous electric blasting caps, while each of the 2nd, 4th, and6th holes was initiated by means of A type short perioddelay electricblasting caps, all caps being fired in a single series. The results ofthis blast were better even than those of Example .I and thisalternating method of blasting is usually preferreifor it insures aneffective separation in firing time between all adjacent holes.

Example III Another blast was made in the same quarry in which those ofExample I and II were made. The same general loading scheme was employedexcept that in this lastblast there were only six 110165;; The holes inthis blast; however, were loaded with dynamite of two different lowvelocities, a dynamite of lower velocity (about 3,600 feet per secondmeasured unconfined in PA by 8 inch cartridges) being employed in holes1, 3, and 5 and a dynamite of a higher velocity (about 6,800 feet persecond measured unconfined in 1%; by 8 inch cartridges) being employedin holes 2, 4, and 6. Holes 1, 3, and 5 were initiated by means of Atype short delay electric blasting caps and holes 2, 4, and 6 wereinitiated by means of instantateous electric blasting caps.

This blast appeared to move out unusually slowly and produced apeculiarly muiiled sound. The breakage produced was very good.

Example .I V

The method of shooting cf'this example produces adequatejseparatioh offiring times between'adjacent holes and also avoids simultaneous firingeven of alternate holes. This blast came out welland the breakageproduced was exceptionally good. I

'E'ramplc V y In another limestone quarry a blast of thirty four holeseach about 5 /2 inches in diameter was made. In this blast the hol'es"were divided into two parallel rows of seveneteen holes. The dynamitemp1cyed was packaged in five inch diameter 25 pound cartridges. In thefront row beginning with the first hole, alternating holes wereinitiated by means 'oi type short period delay electric blasting caps'and beginning with the second hole alternating'hole's in the vfrontro'wwe're initiated by m an of instantaneous electric blasting c'ap's.In the back row each hole was initiate by mea s of B type short perioddelay electric blasting caps. This blast was also highly successful andproduced a degree of breakage notordinarily ex erienced at thislocation.

Exam le T7;

in the limestone uarry of Example V, a hole blast was made in each holeof which the charge consisted of a main charge and onedeck charge.Beginning with the first hole the main charge in each alternatin holewas initiated by means of an A type short delay electric blast ing capand beginning with the second hole each main charge was initiated bymeans of an instantaneous electric blasting cap. 'In this blast,however, each deck charge wasfir'ed by means cf an A type short delayelectric blasting cap, no detonating fuse being employed.

Example VII In a mining operation in which a bank of over burden wasstripped from a coal seam a single row of fourteen five inch horizontalholes averaging 39 feet in length were drilled. Each hole was chargedwith a main charge of low velocity dynamite and a deck charge ofdynamite of somewhat higher velocity. Beginning with the first hole eachalternate main charge was initiated by means of instantaneous electricblasting caps and beginning with the second hole each alternate maincharge was initiated by means of A type short delay electric blastingcaps. The deck charges in alternating holes, beginning with the firsthole, were initiated by means of A type short delay electric blastingcaps. Beginning with the second hole the deck charges were initiated 'bymeans of B type short delay electric blasting caps. The breakageproduced in this blast was exceedingly good.

" Example VIII In a granite quarry having a face about 20 feet inheight, 145 vertical holes were arranged in three parallel rows. Eachhole was about 2 inches in diameter, and about 223 feet deep. The holeswere about five feet apart, and each had been sprung with one 1%; by 8inch gelatin dynamite cartridge. They were loaded with a total of 1800pounds of 1 by 12 inch gelatin dynamite cartridges. In the front rowbeginning with the first hole, each alternate hole was initiated bymeans of instantaneous electric blasting caps, and beginning with thesecond hole in the front .row each alternate hole was initiated by meansof A type short delay electric blasting caps. Each hole in the secondrow was initiated by meansof A, type short delay. electric blastingcaps. The third-row of holes was initiated by means of B type shortdelay electric blasting caps. This blast showed amarked improvement inbreakage over'conventional prior blasts using all instantaneous caps. Aparticularly great improvement obtained as a result of the blast of thisexample was practical elimination; of backbreak which had beenparticularly seriousat this quarry. w

p EmampleIX' 7 In-alimestone mine the'face of a tunnel was drilled withfifteen 1 /2 inch diagonal holes in the general manner shown in Figures4; and 5 of"-the 'drawing. Each hole. was approximately feet in depthand aboutdfeet of tamping was used after the charge in each hole. Atotal of about-59 pounds of 40%. gelatin dynamite was contained man theholes. vBeginning with the first hole, each alternate hole was fired bymeans of an.A typeshort delay electric blasting cap having an averagedelay .period of about I 40 milliseconds and each alternate holebeginning with the second hole was fired by means of an instantaneouselectric blasting cap. The results of this blast showed much improvementover prior conventional type blasts. Normally about seventy blocksrequiring secondary blasting were produced. Only twenty-five requiredsecondary blasting'as a result of this blast.

Example X a In another limestone quarry a further type of blasting inaccordance withthe invention was performed- A row of six inch holes wereeach loaded with 75 pounds of 50% strength ammonia gelatin dynamite and100 pounds of 60% strength ammonia gelatin dynamite. Each hole was feetdeep and the holes were spaced 12 feet apart and 12 feet from the faceof the quarry. The first six successive holes were each initiated bymeans of instantaneous electric blasting caps. The next seven successiveholes in the row were initiated by means of A type short delay elec- Ltric blasting caps, and the last seven holes were initiated by meansof Btype short delay electric blasting caps. This blast was productiveofvery goodresults, and while the breakage was good all along the line ofholes, it was noted to be particularly good in front of the holes in anelectric blasting cap within the hole or the first detonation of fusewithin the bore hole.

where-a line'of detonating fuse running into the bore hole is reliedupon to'initiate the hole.

What is claimed is: V 1. A process of cooperative multiple bore holeblasting, wherein the blast is primarily detonated by electric blastingcaps, which comprises detonating a'row of at least three charged boreholes generally aligned so as on firing to break away a face and form anew face therebehind, the

charges in the adjacent of at least three successively adjacent boreholes in said row being detonated attimes separated by fromz to 150milliseconds and'within about 300 milliseconds of the time ofelectricalactuationv of the first firing blasting cap.

.2. A process of cooperative multiple bore hole blasting wherein a rowof at least three charged bore holes is generally aligned so as onfiringto break away a face and form a new face therebehindwhichcomprises detonating the charges in alternate bore holes substantiallysimultaneously, the chargesin intermediate bore holes beingidetonated attimes separated from 2 to 150 millisece onds from the time of detonationof charges in adjacent bore holes and within approximately 300milliseconds of the time of actuation; of-the detonation initiator inthe first firing bore hole.

3. A process of cooperative multiple bore hole blasting which comprisesdetonating a' row ofat least three charged bore holes generally alignedso as on'detonating to break away a face and form a new facetherebehind, the charges in the adjacent of at least three successivelyadjacent bore holes in said row being detonated; at

times separated by from 2 to 150 milliseconds and within approximately300 milliseconds of the time of actuation of the detonation initiator inthe first firing of said last mentioned bore holes, said time separationof from 2 to 150 milliseconds being suflicient to provide a high degreebreakage on the burden but insuflicient to destroy the cooperativeefiect of multiple hole blasting on the burden among said last mentionedholes.

4. A process according to claim 1 wherein said row is generally parallelto said face.

5. A process according to claim 2 wherein said charges in intermediatebore holes are detonated at times separated by fromapproximately 20 toapproximately milliseconds from the time of detonation of adjacent boreholes.

6. A process of cooperative multiple borehole blasting wherein a row ofat least three charged bore holes is generally aligned so as on firingto break away a face and form a new face therebehind which comprisesdetonating the charges in' alternate bore holes substantiallyinstantaneously, the charges in intermediate holes being detonated fromabout 20 to about '75 milliseconds from the time of detonation ofcharges in adjacent bore holes.

7. A process according to claim 3 where said time separation is a periodfrom approximately 20 to approximately '75 milliseconds.

8. A process according to claim 3 wherein the charges in said boreholesare detonated in two different sets, each hole of one set alternating inposition with a hole of a second set and each hole of saidfirst-mentioned set firing before each hole of said second-mentionedset.

9 A process according to claim 3 wherein the charges in eachsuccessivelyadjacent bore hole in said row are detonated sequentially.

10. A process according to claim 3 wherein said time separation is aperiod of from approximately 20 to approximately 75 milliseconds, andwherein the charges in said bore holes are detonated in two differentsets, each hole of one set alternating in position with a hole of asecond set and each hole of said first mentioned set firing before eachhole of said second mentioned set.

11. A process according to claim 1 wherein said time separation is aperiod from approximately 20 to approximately 75 milliseconds andwhere-' 13 in said electric blasting caps are simultaneouslyelectrically actuated.

12. A process according to claim 1 wherein said time separation is aperiod from approximately 20 to approximately 75 milliseconds andwherein the charges in said bore holes are detonated in two difierentsets, each hole of one set alternating in position with a hole of asecond set and each hole of said first mentioned set firing before eachhole of said second mentioned set.

13. A process according to claim 2 wherein the blast is primarilyinitiated by electric blasting caps which are electrically actuatedsimultaneously.

14. A process of cooperative multiple bore hole blasting which comprisesdetonating a row of at least three charged bore holes generally alignedso as on detonatingto break away a face and form a new face therebehind,the charge in the adjacent of at least three successively adjacent boreholes in said row being detonated at times separated by fromapproximately 20 to approximately 75 milliseconds, the charges in saidlastmentioned bore holes being detonated in two different sets, eachhole of one set alternating in position with a hole of a second set andeach hole of said first-mentioned set firing before each hole of saidsecond-mentioned set, said time separation of from approximately 20 toapproximately milliseconds being sufiicient to provide a high degreebreakage on the burden but insufficient to destroy the cooperativeeffect of multiple hole blasting on the burden among said lastmentionedholes.

DAVID M. MCFARLAND.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1 821,883 Du Pont May 29, 19061,570,733 Eschbach Jan. 26, 1926 2,239,123 Stoneking Apr. 22, 19412,475,875 Burrows et al July 12, 1949 OTHER REFERENCES

